Mascara is the latest in a “Write code in X and translate it to JavaScript” system to be launched.

Mascara calls out systems like GWT, Script#, and HotRuby and says…

Mascara has a different approach, because we actually like JavaScript. The core of JavaScript is well-designed, powerful and flexible, and in many ways a more modern design than C# and Java. ECMAScript 4 is not a replacement for JavaScript, rather it is a set of powerful extensions to the base language, while still fully backwards compatible with classic JavaScript.

This means you can keep using all your existing JS-code, or gradually upgrade your code step-by-step to ES4. ES4 is actually specifically designed to allow gradual upgrade from classic JavaScript to ES4.

You can keep using your favorite JavaScript libraries like jQuery, Prototype or YUI and the immense amount of JavaScript code available on the web, while still making your own code more robust and structured by utilizing the ESMAScript 4 type verification and constructs like classes and namespaces.

JavaScript have gotten a reputation for incompatibilities across browsers. This is somewhat unfair, since JavaScript the language is quite consistent across browsers. The incompatibilities are caused by differences in the DOM and CSS implementations, which indeed are frustratingly inconsistent across browser. But that problem is not solvable at the language level, but rather at the library level, where jQuery or the alternatives will hide the browser incompatibilities for you.

So, if you like JavaScript, but want more of it, ECMAScript may be for you.